1. Field of the Invention
The present invention relates to a superconducting cable conductor with a superconducting material based on rare earth barium cuprates, the superconductor material being applied in layer form on a tape-type substrate. In particular, the invention relates to a superconducting cable conductor of this type for AC applications.
2. Description of the Prior Art
Superconducting cable conductors are usually constructed from a generally cylindrical carrying element with superconducting wires wound helically thereon as superconducting conductor elements.
The carrying element may comprise a conductive or nonconductive material and is usually configured in flexible fashion.
The superconducting conductor elements are wound 20 helically on said carrying element in one or more layers. Each individual layer is obtained by a plurality of, for example tape-type, superconducting conductor elements being wound next to one another onto the carrying element or onto a layer that has already been wound onto the carrier element.
Thus, EP 0 650 205 52 describes a multilayered superconducting cable conductor for AC applications, multifilament wires being used as conductor elements.
The multifilament wires contain a multiplicity of 30 filament-type cores comprising a superconductor material which are embedded in a matrix comprising a normally conducting metal, in particular silver. In order to avoid AC losses on account of eddy currents and coupling currents, insulating layers comprising an insulating material are provided between the individual layers comprising superconducting wires.
The superconducting wires are obtained by filling for example pulverulent starting material, which can be converted into the desired superconductor material by means of suitable thermal treatment, into a casing comprising a normally conducting metal, preferably silver. The casing filled with the pulverulent starting material is subjected to a plastic deformation with drawing and rolling to form a long filament having a small diameter and is subsequently sintered. The individual filaments obtained are combined to form a bundle comprising a multiplicity of individual filaments and passed together into a further casing, which is in turn subjected to a plastic deformation and sintering. A superconducting multifilament wire with the desired number of filaments in a metal matrix is obtained as a result. The finished multifilament wire preferably has a tape form.
The superconductor material acquires the desired 20 high orientation as a result of the treatment described above, the crystallographic c axis essentially extending perpendicular to the current flow direction and the a-b plane extending parallel to the current flow direction. The orientation should preferably be as homogeneous as possible over the entire extent of the superconducting material.
Depending on the diameter of the carrying element onto which the multifilament wire is wound, and on the lay length of the individual turns, forces as a result of bending elongation and tensile stress are exerted on the wires during the winding process and in the unwound state. This may result in an impairment of the orientation of the superconducting phase and thus in a reduction of the superconducting properties.
In order to be able to obtain the greatest possible freedom with regard to the diameter of the carrying element and the lay length of the winding and thus with regard to the cable construction, a superconducting cable is desirable, therefore, in which no degradation of the superconducting wires occurs even in the case of a relatively high degree of bending for example in the case of a small diameter of the carrying element and/or a small lay length, and relatively high tension.